Pathogenic fungi can be divided in two categories: fungi that are able to induce diseases in normal subjects and less invasive fungi that are able to produce diseases only in critically ill hosts. In the past two decades there was a significant increase in the incidence of invasive opportunistic fungal infections and associated morbidity and mortality. This is mainly due to the major advances in modern medicine that have increased the survival of critical patients such as those in intensive care units (ICU) with intravascular and urinary catheters, total parenteral nutrition and hemodialysis or connected to ventilatory systems.
Candida species commonly cause nosocomial blood stream infections among patients in the ICU. The UK hospitalized incidence of candidemia is about 3 per 100,000 bed days, and 40% to 52% of all cases occur in ICU (Schelenz S., J. Antimicrob. Chemother. 2008; 61, Suppl 1, 31-34). This kind of mycoses is frequently associated with considerable morbidity and mortality.
The attributable mortality rate is about 38%, although it can vary between 5% and 71%. During recent years there was a rising incidence of invasive pulmonary aspergillosis in patients admitted to ICU. The disease incidence ranges from 0.3% to 5.8% with an overall mortality rate exceeding 80% (Trof R. J. et al, Intensive Care Med., 2007; 33, 1694-1703). Critically ill patients are at risk to develop disturbances in immunoregulation during their stay in the ICU, which render them more vulnerable to fungal infections. Risk factors such as chronic obstructive pulmonary disease, prolonged use of steroids, advanced liver disease, chronic renal replacement therapy, near-drowning and diabetes mellitus have been described.
There was a dramatic increase also in the number of immunocompromised patients especially in the fields of solid organ and bone marrow transplantation, autoimmune syndromes, acquired immune deficiency syndrome (AIDS) and oncology.
About 40% of bone marrow transplant population develops invasive fungal infection (Khan S. A., Wingard J. R., Natl. Cancer Inst. Monogr. 2001; 29, 31-36). Candida and Aspergillus species are the most common pathogens responsible for nosocomial superficial and invasive mycoses in hematologic malignancies and bone marrow transplanted patients. In these patients the mortality associated with the systemic candidosis is very high (50-90%). Regarding solid organs transplantation, infective complications are more frequent in lung-transplanted patients. In addition to the immunosuppressive regimen, the increased susceptibility is mainly due to the constant exposure to the external environment. Parallel to immunosuppressive treatment intensity, invasive fungal infection may occur during the first days after surgical operation, its frequency is highest in the first two months and decreases after 6 months but it can occur also years after transplantation (Hamacher J. et al, Eur. Respir. J., 1999; 13, 180-186).
Invasive fungal infections are also frequent in other kind of solid organ transplantation such as kidney and liver transplants for which incidence of 5 to 50% are reported (Dictar M. O. et al, Med Mycol., 2000; 38 Suppl. 1, 251-258).
Mycoses are one of the major causes of morbidity in patients with AIDS and the incidence and severity of these infections increase with disease progression and the consequent impairment of T-cell-mediated immunity. The incidence of the different mycoses is closely related to the endemic opportunistic fungi present in the area of residence. Generally speaking the most frequent mycoses that affect AIDS patients are histoplasmosis, blastomycosis, coccidioidomycosis and paracoccidiomycosis (Sarosi G. A., Davies S. F., West J. Med., 1996; 164, 335-340).
Mucosal Candida infections are also extremely common. In normal patients all these mycosis are usually self-limited but in immunodepressed patients become highly invasive resulting in progressive and widespread dissemination.
Moreover, the increase of mycosis caused by organism resistant to current therapies became evident over recent years. This phenomenon is particularly evident for fungal infections caused by Candida albicans and fluconazole and other azoles (Bastert J. et al, Int. J. Antimicrob. Agents, 2001; 17, 81-91).
The antimycotic drugs currently available are not fully satisfactory due to their limited activity spectrum and to the heavy side effects associated to their use. The polyene drug Amphotericin B, for example, is active against Aspergillus, Zygomycete and other molds anyway, and due to its toxicity the licensed dosage for treatment of invasive mycosis is 3-5 mg/kg per day. In highly immunocompromised patients with invasive aspergillosis, liposomal encapsulated Amphotericin B, daily administered at 3 mg/kg, gave a favorable response in 50% of patients and 12-week survival rate of 72% (Cornely O. A. et al, Clin. Infect. Dis., 2007; 44, 1289-1297). The drug induced nephrotoxicity and hypokalemia in 14-16% of the patients. When daily administered at 10 mg/kg, Amphotericin B did not give any additional benefit and caused higher rates of nephrotoxicity (31%).
Azoles, introduced in the second half of the 1970s, are blockers of ergosterol synthesis. The use of the drugs belonging to this family is limited by their narrow spectrum of activity. Voriconazole, for example, is more active than Amphotericin B for the treatment of invasive aspergillosis but has no activity against zygomycetes (Johnson L. B., Kauffman C. A., Clin. Infect. Dis., 2003, 36, 630-637). The azoles employment is also limited by the induction of several side effects. Azoles interact with mammalian p450 enzymes resulting in interference with the metabolism of other drugs and, in addition, some azoles such as ketoconazole are able to block the cardiac potassium channel Kv1.5 causing Q-T prolongation and ‘torsade de pointes’ (Dumaine R., Roy M. L., Brown A. M., J. Pharmacol. Exp. Ther., 1998; 286, 727-735).
Allylamines such as Terbinafine bind to and inhibit squalene epoxidase resulting in a block of ergosterol synthesis. These drugs are very potent against Dermatophytes while their activity against Candida species is very poor. In some cases treatment with allylamines is followed by severe cutaneous adverse reactions. A recent multinational case-control study (euroSCAR) (Sidoroff A. et al, Br. J. Dermatol., 2007; 15, 989-996) revealed that Terbinafine systemic treatment is strongly associated with the development of an acute generalized exanthematous pustolosis (AGEP). This disease is characterized by the rapid occurrence of many sterile, nonfollicular pustules, usually accompanied by leucocytosis and fever. AGEP is generally attributed to the patient treatment with particular drugs and seems to be related to an altered T cells activity. Terbinafine treatment might also induce dermatomyositis, a severe autoimmune connective tissue disease characterized by erythema, muscle weakness and interstitial pulmonary fibrosis (Magro C. M. et al, J. Cutan. Pathol., 2008; 35, 74-81). In addition, as a variety of antifungal medications, Terbinafine might cause severe liver injuries (Perveze Z. et al, Liver Transpl., 2007; 13, 162-164).
Griseofulvin is a benzofurane introduced in 1960 for the treatment of dermatophyte infections. The compound induces its fungistatic activity by interfering with microtubule production. Griseofulvin displays limited activity in the treatment of onychomycoses and frequently causes severe side effects such as nausea, diarrhea, headache, confusion and fatigue (Korting H. C. et al, Antimicrob. Agents Chemother., 1993; 37, 2064-2068) that can cause the treatment discontinuation.
The two N-Hydroxy pyridones, Ciclopirox olamine and Octopirox, seem to mainly act by chelating polyvalent cations, resulting in the inhibition of the metal-dependent enzymes. They are employed against different fungal infections but their use is limited to topical treatment.
The echinocandins (Caspofungin, Micafungin, Anidulafungin) are semi-synthetic lipo-peptides and are the most recently introduced antimycotic drugs. They act by non-competitively inhibiting β-(1-3)-Dglucan synthase, an enzyme essential for the maintenance of the cell wall and are mainly used for intravenous treatment of invasive candidiasis and aspergillosis. They are fungicidal against yeast but only fungistatic against filamentous fungi; in addition, they are quite inactive against dimorphic fungi such as Blastomyces and Histoplasma. Echinocandins are generally well tolerated but animal reproduction studies showed adverse effects on fetus. For this reason FDA lists echinocandins as a pregnancy-risk category (http://www.fda.gov/medwatch/SAFETY/2004/mar_PI/Cancidas_PI.pdf; http://www.fda.gov/medwatch/safety/2007/Aug_PI/Mycamine_PI.pdf). WO98/11073 (U.S. Pat. No. 6,310,211) discloses 8-hydroxy-7-substituted quinolines as anti-viral agents.
US2003/0055071 discloses a generic class of compounds having HIV integrase inhibitory activity. As a matter of fact, most of the specific compounds disclosed in this reference bear a naphthydrinyl residue.
EP1375486 discloses nitrogen-containing heteroaryl compounds having HIV integrase inhibitory activity. N-benzyl-8-hydroxyquinoline-7-carboxamide. WO2008/14602 discloses quinoline derivatives active as CLK-1 inhibitors. EP1669348 discloses antifungal agents defined by a very broad formula which includes certain secondary amides.
From what described above, it is evident that the clinical need for efficacious antifungal drugs has dramatically increased in the few last years. Unfortunately the drugs actually available are not satisfactory due to their narrow spectrum of action, pharmacokinetic properties and severe side effects.